dist: drop legacy control group parameters

Since we dropped CentOS7 support, now we can drop legacy control group
parameters which is deprecated on systemd v252.

dist/common/systemd/scylla-helper.slice

@@ -15,10 +15,3 @@ MemoryHigh=4%
 # MemoryMax is the OOM point. As Scylla reserves 7% by default, the other two percent goes to
 # the kernel and other non contained processes
 MemoryMax=5%
-# Systemd deprecated settings BlockIOWeight, MemoryLimit and CPUShares. But they are still the ones used in RHEL7
-# Newer SystemD wants MemoryHigh/MemoryMax, IOWeight and CPUWeight instead. Luckily both newer and older SystemD seem to
-# ignore the unwanted option so safest to get both. Using just the old versions would work too but
-# seems less future proof. Using just the new versions does not work at all for RHEL7/
-MemoryLimit=5%
-CPUShares=10
-BlockIOWeight=10

scylla_post_install.sh

@@ -41,18 +41,6 @@ if [ $MEMTOTAL_BYTES -lt 23008753371 ]; then
 [Slice]
 MemoryHigh=1200M
 MemoryMax=1400M
-MemoryLimit=1400M
-EOS
-
-# On CentOS7, systemd does not support percentage-based parameter.
-# To apply memory parameter on CentOS7, we need to override the parameter
-# in bytes, instead of percentage.
-elif [ "$RHEL" -a "$VERSION_ID" = "7" ]; then
-    MEMORY_LIMIT=$((MEMTOTAL_BYTES / 100 * 5))
-    mkdir -p /etc/systemd/system/scylla-helper.slice.d/
-    cat << EOS > /etc/systemd/system/scylla-helper.slice.d/memory.conf
-[Slice]
-MemoryLimit=$MEMORY_LIMIT
 EOS
 fi